C-O-H gases

This system has been treated in detail by French (1966), Skippen (1967) and Eugster and Skippen (1967). Bulk compositions for selected f (O2) s have been tabulated by Deines al. (1974). The principal gas species are H2O, H2f 2 CO2/ CO and CH.  

Such buffered assemblages are quite common in nature and make contact aureoles of impure carbonate rocks one of the best areas to study the evolution of metamorphic fluids, because fluid compositions are essentially controlled by the mineral reactions. Progressive metamorphism initially leads to a rapid enrichment in CO2/ because the talc and tremolite reactions consume H2O and release CO2. At higher temperatures, water enrichment can take place by the decomposition of tremolite to diopside and/or forsterite. Changes in the compositions of the solids will affect the fluid ratios, and in fig. 6 the compositional changes of coexisting calcite and dolomite as a function of temperature have been taken into account. 

In the presence of graphite, H2O and CO2 are still important, but CHj, CO and H also become significant. French (1966) and Skippen (1967) have analyzed the C-O-H system in equilibrivim 

one degree of freedom remains and has to be removed either by stipulating a bulk composition, a fixed f(H2) or f(02). The explicit solution for fixed f(02) in terms of f(H2O), can be obtained from V T —1 

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A recent experimental study on carbon isotope fractionation in the system CO2-CH4 (Horita 2001) showed that results of theoretical calculations by Richet et al. (1977) are accurate (to 0.9%o) over the temperature range from 200 to 600°C. However, in the application of fractionation data for C-O-H gases, perhaps a more important question is... 

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